1. Field of the Invention
The invention relates to a timepiece, in particular a wristwatch with a constant-force device for acting on an oscillating system, the constant force device having a switching unit and a tensioning module.
2. Description of the Related Art
The switching unit periodically controls tensioning of a secondary spring-energy store of the tensioning module by a spring barrel forming a primary spring-energy store, the periodic control of the switching unit taking place by means of a cam plate which can be driven in a permanently rotatable manner.
By virtue of such constant-force devices, the primary spring-energy store, rather than acting directly on the oscillating system, periodically tensions the secondary spring-energy store, which then acts on the oscillating system.
The level of force acting on the oscillating system is thus, to the greatest possible extent, constant, which results in a high level of accuracy for the timepiece.
A known timepiece with a constant-force device has the problem of a high level of force being lost over the transmission path from the primary spring-energy store to the secondary spring-energy store, which also drives the cam plate, so that the torque acting on the cam plate is relatively low.
In order to achieve a sufficient torque, the initial force of the primary spring-energy store therefore has to be set at a high level.